1. Field of the invention
The present invention relates to a device for pushing and pulling an accessory instrument used in a manufacturing process especially such a device which pushes and pulls an accessory instrument horizontally by means of finite chains functioning as thrust and tension elements driven by hydraulic actuators, In this specification, the term "accessory instrument" includes a clamp for fixing a metallic mould on a bolster, for example. or a slider of a press, or as a means for fixing a work pallet on a table of a machining tool, or apparatus functioning as a hook for carrying a metallic mould or a work pallet between a feeding table and a machine such as a press, an injection molding machine, a machining center, etc. The term `finite chain` refers to a chain which is allowed to kink in one direction but not the other opposite direction beyond linear alignment of adjacent links.
2. Background Art
When a finite chain is used as a horizontal thrust and tension element to push and pull an accessory instrument, such as a clamp, it is required to locate the chain within its housing in a vertical direction. The chain type jack device is therefore basically provided with a vertically elongated housing having an opening at an upper or lower end of one lateral side thereof through which the finite chain is fed. The chain is housed vertically in said case and kinks to extend through the opening in the horizontal direction. A hydraulic actuator drives the chain vertically within the housing to pass the chain through said opening in order to push or pull the accessory instrument in lateral directions, which instrument is connected to one end of the chain extending through the opening.
A known device for pushing and pulling an accessory instrument is descried, for example, in U.S. Pat. No. 4,326,624, wherein a finite chain is driven by a sprocket 28 actuated by a hydraulic motor to function as a thrust and tension element.
However, the use of a hydraulic motor is disadvantageous for several reasons. First, it is expensive and complex in structure. Second, it is subject to damage when subjected to acceleration greater than 30 G. Thirdly, it is subject to loss of power to compensate for the leakage of fluid in the motor when the instrument is maintained in the working position or the retreated position. Fourth, it must be provided with a braking system to eliminate the loss of power problem mentioned above.